Apparatus for printing on both sides of the lids of egg cartons

ABSTRACT

A rotary cylinder, for example having an offset blanket attached is arranged for engagement with a surface panel raised above a border rim to be printed; a segmental cylindrical element having cylindrical surface portions and, for example, an offset blanket attached to the surface portion is located for engagement with the surface of the obverse side of the panel to be printed. The leading and trailing faces of the segments extend from the obverse surface in a general transverse direction with respect to the center of the cylindrical element, at angles with the faces (with respect to a tangent at the point of junction of the faces and the cylindrical surface) which are so selected that the segmental element may enter into the hollow or cavity formed by the obverse surface and the rim. Ink transfer means, such as ink trains, printing cylinders, and the like are located to be engaged by the segmental cylindrical surfaces. Both the cylindrical element as well as the segmental cylindrical surfaces are driven in synchronism, preferably at a slightly faster speed than the supply and removal speed of the objects to be printed so that any possible drag on the objects by the supply, and removal apparatus, during printing, is avoided.

ll'ite States atent [191 Provan [54] APPARATUS FOR PRINTING ON BOTH SIDES OF THE LIDS OF EGG CARTONS [75] Inventor: Alexander R. Provan, Canandaigua,

[73] Assignee: Mobil Oil Corporation, New York,

221 Filed: Dec. 3, 1970 [21] Appl. No.: 94,658

Primary Examiner-Robert E. Pulfrey Assistant Examiner-Clifford D. Crowder Attorney-Oswald G. Hayes, Andrew L. Gaboriault and Mitchell G. Condos [5 7] ABSTRACT A rotary cylinder, for example having an offset blanket attached is arranged for engagement with a surface panel raised above a border rim to be printed; a segmental cylindrical element having cylindrical surface portions and, for example, an offset blanket attached to the surface portion is located for engagement with the surface of the obverse side of the panel to be printed. The leading and trailing faces of the segments extend from the obverse surface in a general transverse direction with respect to the center of the cylindrical element, at angles with the faces (with respect to a tangent at the point of junction of the faces and the cylindrical surface) which are so selected that the segmental element may enter into the hollow or cavity formed by the obverse surface and the rim. Ink transfer means, such as ink trains, printing cylinders, and the like are located to be engaged by the segmental cylindrical surfaces. Both the cylindrical element as well as the segmental cylindrical surfaces are driven in synchronism, preferably at a slightly faster speed than the supply and removal speed of the objects to be printed so that any possible drag on the objects by the supply, and removal apparatus, during printing, is avoided.

5 Claims, 9 Drawing Figures PATENTEDHAYZSIHYS 3 735,697

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P] I25 v 62 FIG. 5 l2! FIGS PATENTEB HAYZ 9 I975 sum 3 UF 3 FIG. 9 I

I APPARATUS FOR PRINTING ON BOTH SIDES OF THE LIDS OF EGG CARTONS The present invention relates to rotary printing apparatus specifically arranged to print on surfaces, or surface panels within a cavity or hollow and referred to as concave surfaces, and more specifically to print on the inside of the lids of egg cartons made of any material, and especially made of expanded plastic material such as expanded polystyrene.

Simultaneous printing on two sides is known. This process, called perfect printing may utilize a pair of offset printing cylinders, each one engaged with one or more (depending on the number of colors desired) ink trains and letterset relief cylinders. In essence, the impression cylinder, normally backing up a printing blanket cylinder is replaced by another printing blanket cylinder, having its own letterset and ink train associated therewith. To prevent smear of printing, either on the top, or on the bottom surface of the sheet, the drives of the blanket cylinders and letterset relief plate cylinders must be synchronized.

Simultaneous, double face printing can also utilize other processes, in which the impressions element, such as a cylinder, backing up the printing element can be replaced by a printing element.

Paper, cardboard or the like, to be printed usually has a predetermined thickness and the spacing between upper and lower printing elements or between an upper printing element and an impression cylinder, if used, is determined by the thickness of the material on which printing is desired. Difficulties are experienced if the material to be printed is non-absorbent, and particularly if the material is subject to wide variations in thickness and, additionally, has a surface which is somewhat abrasive so that only hard impressionmaterial can be used.

When printing on plastic egg cartons, such as expanded polystyrene egg cartons, the machine must accept material having a gauge variation which may easily exceed 20 percent, since the thickness of plastic, expanded material is controllable only with great difficulty, and involves expense usually not warranted with a throw-away item, such as an egg carton. The nominal thickness of egg carton material in the cover section, i.e., the area to be printed,may be about 0.100 inch, and the thickness variation could easily be plus or minus 0.01 inch. The material, although somewhat resilient and accepting some crushing against a backup, is, however, somewhat brittle. In actual practice it has been found that letter presses are less desirable for large quantity printing on the lids of egg cartons since the printing pattern wears out, unless made of hard material, which is expensive. Flat bed printing by means of rubber plates has not been found satisfactory, since the rubber plates are too soft, leave a poor impression, and wear excessively. Offset printing utilizinga blanket cylinder, for example, a standard 80 durometer rubber blanket has been found satisfactory.

When it is intended to print on the inside of a carton, by means of an offset cylinder, the problem arises that the blanket cylinder cannot engage the surface within the depth of the carton and clear the edge rim. Yet, to effect printing a blanket cylinder must enter the cavity, or hollow of the carton lid as it travels between the blanket cylinders.

It is an object invention to provide a printing apparatus which is capable of printing within the hollow of a concave surface, and more particularly on both sides (that is, the convex, as well as the concave) surface of an article to be printed, and which can print on nonabsorbent, compressible material subject to wide size variation, such as the lids of plastic egg cartons, and particularly of foam plastic egg cartons.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, a cylindrical segmental element is located to engage the inner, or hollow or concave surface to be printed, backed up by a rotating cylinder in synchronous drive engagement with the other surface, that is the outer, or raised, or convex surface. The rotating cylinder engaging the convex surface itself may be the blanket cylinder of an offset printing system, known by and of itself. The segmental cylindrical element has a segmental cylindrical surface with leading and trailing faces cut away from the cylindrical surface and extending from the surface in a general transverse direction with respect to the center of the segmental cylindrical element. The angles formed by the faces with respect to a tangent of the segmental cylindrical elements, at the point of juncture with the faces, are so-selected that the faces will clear the rim of the carton and the element can enter, with clearance, into the hollow of the concave surface as it is being fed over the segmental element. The segmental cylindrical element is provided with a printing transfer device, such as a letterset relief plate or, preferably, with an offset blanket which is, in turn, engaged by the letterset relief plate and an ink train, so that printed indicia can be transferred to the inside, that is, the concave surface. More than one combination of letterset relief plate and ink train may be 'located in engagement with the printing blanket on the cylindrical element.

If a compressible material, such as expanded polystyrene, pulp cartons, or any other compressible material used as the lid for an egg carton, is to be printed, then the gap between the top cylinder engaging the convex surface, or its printing blanket if it is an offset printing cylinder, and the cylindrical surface of the cylindrical element is so arranged that the material on which printing is to take place is somewhat compressed. Depending on the nature of the material it may be substantially compressed, for example in the order of 50 percent of its nominal thickness. Such compression, occurring only momentarily, does not destroy the material and permits simultaneous printing, that is perfect printing on both sides of sheet material subject to wide thickness variations.

In the printing of egg cartons, the cartons are preferably fed to the printing stations opened, that is, with the lids arranged so that the concave surface does not face the egg holding cavities. In one form of apparatus, transport is by means of a pusher arrangement, for example upstanding projections secured to a transport chain. The printing speed, that is, the circumferential speed of the upper, and lower blanket cylinders is'then selected to be slightly higher than the linear transport speed of the transport mechanism for the egg cartons. The egg cartons, upon being pushed by the projection, will be fed over the printing cylinders which, because of their higher speed, will pull them away from the feed mechanism and deposit them, after printing, .at an exit station ready to be picked up by a projection coming at a slightly lower speed. Thus, any drag on the cartons by the transport mechanism is avoided and the printing cylinders will print on the cartons without possible BRIEF DESCRIPTION OF THE DRAWINGS Advantages of the invention will become apparent to those skilled in the art from the following description considered in conjunction with the drawings wherein:

FIG. 1 is a perspective general view, highly schematic, of a combined top and bottom printing unit for perfect printing on the lids of egg cartons;

FIG. 2 is a schematic side view, omitting all supporting structural elements and transport and drive mechanisms, illustrating a 4-color printing system for the top of the lid and a 2-color printing system for the bottom of the lid;

FIGS. 3, 4 and 5 are three fragmentary detailed views, highly schematic, showing sequential steps in the engagement of the surfaces to be printed by the top and bottom cylinders;

FIG. 6 is a highly enlarged schematic view illustrating printing at the printing position and alignment of the respective elements;

FIG. 7 is a schematic, perspective view of a letterset relief plate and ink train, and illustrating its arrangement within the entire system;

FIG. 8 is a schematic top view of the printing unit and schematically illustrating the transport mechanism; and

FIG. 9 is a schematic fragmentary view of the drive for the letterset relief plate and its adjustment.

DETAILED DESCRIPTION Referring first to FIGS. 1 and 2: an egg carton, C, has a lid structure with a convex outer surface SX and a concave, inner surface SV. The egg carton, its lid and egg holding section spread flat (see FIG. 8) is transported by a follower 60, which may be an upstanding projection or finger, attached to a transport chain 61 along a support table 62. Located along the support table, which forms a transport surface, is a printing unit composed of an upper printing section 10 and a lower printing section 110. The upper printing section comprises a blanket cylinder 20, for example of 12 inch diameter and a group, (four being shown as an example) of printing units each having a letterset relief plate 30 and an ink train 40. A 12 inch cylinder prints two images per revolution on an ordinary egg carton; three images can be printed with an 18 inch diameter cylinder. The diameter of the cylinder is a matter of design, depending on the length of the printed matter, printing and transport speed and the like. In the particular example shown, four letterset relief plates 30R, 308, 306 and 30Y each carry printing patterns in red, black, green and yellow, respectively, to transfer printing indicia such as advertising, identifying and other information items on a rubber blanket 25, which may be in the form of two stripes not shown separately secured to blanket cylinder 20. Neither the ink trains, nor the letterset relief plates or the blanket cylinder need be described in greater detail since all these elements are well known and form part of a rotary offset multi-color 4 printing assembly shown, for example in Paper Film and Foil Converter", Vol. 43, No. 4, Page 114, April 1969.

Ink transferred from the ink train to the convex portions of the letterset relief plate is transferred, with the respective color, to the offset blanket 25 which, in turn, prints on the convex surface SX of the egg cartons C.

To effect printing on the inside hollow of the carton C, that is, .on the concave surface SV of the lid, a segmental cylindrical printing element is provided. The segmental cylindrical element 120 is generally in the shape of a two-pole field element of a dynamo electric machine, in that it comprises a cylindrical section 121, 121, which has leading and trailing end faces 122, 122' and 123, 123', respectively, each angled away from the continuous circumference of the cylindrical sections, extending generally in a direction towards the center of the cylindrical surface and then merging into a central structure 124 which also carries the hub for the entire element 120. The dimension and shape of structure 124 is determined by the material used, for example aluminum, and strength and mechanical requirements; its shape is not critical. A pair of offset blanket strips 125, 125' are applied to the outside surfaces of the cylindrical sections 121, 121'. The overall diameter between the outside surfaces of the blanket strips 125, 125' is the same as the diameter of the blanket 25 applied to the blanket cylinder 20.

Blanket cylinder 20, and segmental element 120 are driven in synchronism, as schematically illustrated in FIG. 2 by a suitable drive 26, such as a chain drive, gearing or the like. Synchronized drives for blanket cylinders and backup, impression cylinders are well known and the drives for the specific type of segmental cylindrical element with the blanket strips attached thereto can be identical to such synchronized drivesv They have, therefore, not been illustrated in detail, but only schematically.

To transfer information to be printed to the blanket strips 125, 125', a pair of letterset relief plates A, 130B, each connected to a standard ink train (only one of which is shown in more than outline form) are provided. More than two such chains of ink train and letterset relief plates may be provided, the number of such letterset relief plates and ink trains depending on the available space and the structural arrangement of the drive. For example, a third letterset relief plate similar to plate 130A or 130B, likewise applied to a cylindrical element can be located between the two ink and transfer systems 140, 130A (or 1308), with only minor redesign of the ink train itself. The arrangement illustrated in FIG. 2 is particularly simple since it permits the use of identical letterset relief plates on plate cylinders and ink trains both for the top unit 10, as well as for the bottom unit 110, thus affording economies in manufacture, stocking of spare parts and the like. The number of plate cylinders with letterset relief plates in the top, as well as bottom units will depend, thus, on printing requirements, available space, and cost. For commercial applications, two colors for the bottom may be sufficient. This, in effect, gives a three-color choice since the base material of the egg carton itself supplies one of the contrasting colors which may differ for different sizes of eggs to be contained therein.

FIGS. 3 to 5 illustrate, in sequence, the printing operation. The segmental cylindrical sections 121, 121' are identical, so that the cylindrical element 120 will be balanced. The circumference of the blanket cylinder, and the length of the egg carton lid are so chosen with respect to each other that upon each revolution of the blanket cylinder, two carton lids are printed. The circumferential length of the printed surface on blanket strips 125, 125' likewise is so adjusted that, for the length of printing by blanket cylinder 25, there will always be a portion of a strip 125 or 125' beneath the blanket cylinder 25, so that a portion of the blanket strip of the lower unit 1 will act as the impression cylinder for any material still to be printed from the top blanket cylinder; conversely, of course, the top blanket cylinder will act as an impression cylinder for the material to be printed from the bottom of said blanket. In FIG. 3, the lid of the egg carton C has been fed by the transport follower 60 towards the printing position. The blanket strip 125, which is wrapped over the cylindrical surface and over the leading face 122, and secured thereto by suitable and well known means such as hooks and clamps (schematically shown in FIG. 2 only) is just entering beneath the rim of the lid, that is, within the hollow of the lid structure of the carton C. The angle A which the face 122 makes with a tangent to the cylindrical surface of the segmental cylindrical element 110 is so selected that it is equal to, or preferably slightly less than the angle made by the overlapping end of the lid of the carton C with respect to its flat surface on which material is to be printed, to insure that the relieved face 122 will properly enter within the hollow of the lid of the carton C. In one type of egg cartons, the lid has somewhat sloping sides, making an angle in the order of about 73 with respect to the flat surface of the carton lid to be printed; if the angle of the edge strip which defines the hollow is even steeper, for example 80, straight (90) or even undercut, that is, in excess of 90, then the angle A would have to be decreased beyond that shown in FIG. 3 or, in other words, the edge between the cylindrical surface and the face 122 will have to become more and more pointed. For cartons with more gradually sloping sides, the angle A can be increased. Similar considerations apply to the location and angling of the trailing face 123 which will be a mirror image of the angling of surface 122. The opposite faces H22, 123 will be symmetrical.

FllG. 4 shows the position of the carton just as it is entering the position where printing becomes possible. It 1 will be seen that this is very close to the leading edge of the carton lid. FIG. 5 illustrates the position of the carton lid intermediate as it is being printed. The lid of the carton is supported between the blanket cylinder and the lower segmental cylindrical element. The reason for the relieved surfaces 122, 123 will be apparent from the consideration of the sequential views of FIG. 3 to FIG. 5.

It is difficult to accurately control the thickness of expanded polystyrene, particularly in low cost, throwaway items'such as egg cartons. FIG. 6 illustrates a frag mentary cross-sectional view through the egg carton lid structure during printing. The nominal thickness of the egg carton lid is given a dimension N which, typically, is 0.1 inch. This dimension may vary by 10.01 inch, or more, that is a total variation in the order of 20 percent.

' The outer surfaces of the printing blankets 25, 125 (or 125') are so adjusted, by adjusting the centers of the blanket cylinder 20 or the segmental cylindrical element 120, or both that the dimension P at the printing point effects a reduction in the order of percent or even more, that is, the spacing P would be about 0.05 inch. This substantial compression is possible with expanded plastics; other suitable dimensioning can be readily obtained by a few experiments, in which positive feed of the material to be printed, here the egg car ton lid, by the synchronized motion of the printing cylinder and the segmental cylindrical element, the speed of printing, the ink, and the type of the surface on which printing is to be effected, such as its absorption, abrasion effects, and the like are to be balanced. In a preferred form, the centers of both the printing cylinder 20 and the segmental cylindrical element are so located with respect to each other that they are both spaced equally from a center line CL indicated in chain dotted form in FIG. 6 through the thickness of the egg carton lid. This arrangement provides for effective printing on both sides of the egg carton lid, without smear, without excessive wear on the printing blankets and still enables printing on surfaces subject even to wide variations of thickness. The tolerance, which may be in the order of 20 percent, need not symmetrically extend from both sides of the center line, but greater excursions from the nominal center line, in one direction or the other are possible. The system will be selfadjusting, particularly for material which is as light as egg cartons and in which the lid does not, during printing, rest on a support surface (see FIG. 3-5) although the egg-holding section of the egg carton may well continue to ride on the support surface itself.

The printing speed, that is the linear speed of the cylinder 20 and the segmental cylindrical element 120 is so arranged that it is slightly faster than the linear speed of the transport chain 61 and its follower 60, to prevent possible smearing caused by the pusher 60 skidding the carton through the printing station. If the cartons are pulled, for example by a carton-engaging finger or similar element, then of course the cylinders should operate at slightly lower circumferential speed than the transport speed.

A lid of an egg carton transported by follower 60 hearing, for example, on a hinge area between the egg section and the lid section of the egg carton, as schematically illustrated in FIG. 8, will transport the lid until just about the position of FIG. 4 is reached; at that point cylinder 20 and segmental cylindrical element 120 will engage and grab the lid, propelling it forward while printing on that section of the surface where printing ink has been transferred from the impression cylinders 30, 130. The linear speed of these printing cylinders is slightly faster than the linear speed of the follower 60 so that the egg carton, upon being ejected from between the cylinders and the segmental cylindrical element will be thrown out on the support table 62 to a point slightly in advance of the follower 60. Thus, the follower 60 will positively engage the egg carton at its end, and movement of the egg carton during the printing process is entirely controlled by the printing cylinders. Any drag on the carton by the'transport mechanism is thus avoided and printing can be free of any smears of misalignments.

In ordinary rotary offset presses it is customary to provide an adjustment of the relative rotational position of the plate cylinders and the blanket cylinders (register adjustment). This is particularly important in multi-color work to provide for accurate match for placement of the particular printing indicia on the printing blanket by the respective letter-set relief plates applied to the plate cylinders. The usual system of adjustment utilizes a split, or clampable hub, connected to the cylinder, so that the plate cylinder can be clamped to the drive shaft at selected circumferential positions. The drive shaft itself is positively geared to the machine drive. The upper printing unit can be constructed in accordance with well known designs. Difficulty is, however, experienced in connection with adjustment of the lower units since they are not ordinarily accessible and the alignment of the letterset relief plates, with respect to each other cannot be visually checked. FIG. 9 illustrates an arrangement permitting such adjustment even though the plates cylinders and letterset relief plates 130, together with their ink trains are not accessible due to the intervening structural members supporting the table 62 and the printing units, as well as the drive system 26, which may include a heavy motor. The structural unit of the entire machine is merely schematically indicated at S (FIG. 9) and may have any convenient shape, angle irons, I-beams, cross arrangements, channels and the like. The drive system for the plate cylinder, connected to drive 26 is schematically indicated by arrow 27 and may, for example, comprise gearing, a chain drive, or the like. System 27 is in positive driving engagement with a gear 128 which is connected by means of an elongated hollow shaft 135 to a small clamping hub 129 located at the outside of the structural assembly and unit S. A drive shaft 135' is connected to the respective plate cylinder 130A, or 1308 respectively, and extends through clamping hub 129. At the outside, a hand wheel 136 is provided. Hand wheel 136 and hub 129 may carry respectively alignable index markings. To adjust the position of printing along the length of the inside of the lid, the clamp connection between hub 129 and shaft 135' are loosened and drive shaft 135 can then be rotated freely and independently of the remainder of the apparatus. After clamping of the hub 129 to shaft 135, a test sample is run through the printing machine and, if desired, the printing can be moved forward or rearward, (with respect to the direction of printing), by loosening clamp hub 129 and relatively rotating the hand wheel 136 with respect to the hub 129 and re-tightening. The entire adjustment can thus be affected without moving the otherwise concealed printing units from their location, and without disengaging gear 128 from the drive system 27 which, otherwise, might cause misalignment. Bearings for the hollow shaft interconnecting gear 128 and hub 129, and for the drive shaft 135 have been omitted from the drawings since their location is determined solely by design considerations and will be obvious.

The entire assembly of the letterset relief plates and plate cylinders 130, and inking trains are preferably mounted on a transversely extending slide 137 for removal and servicing as a unit. Moving slide 137 (the counterparts of which within the structural unit have been omitted for simplicity) will cause disengagement of gear 128 with its drive 27. Upon subsequent reintroduction of a single printing unit assembly, after the machine has been moved, realignment may be required. To enable selective engagement of the letterset relief plate on the plate cylinder 130 with the blanket 125, and to adjust the impression pressure, the slide 137 is preferably movable towards and away from the center of the segmental cylindrical element in the direction of arrow 138 (FIG. 2) by means of an eccentric 138, schematically indicated in FIG. 7 and operable by a hand crank 139 which can be locked in predetermined positions, or which may be variably adjustable throughout its movement, so that the entire slide carrying the ink train and plate cylinder assembly can be moved towards and away from the center of the segmental cylindrical element to effect the necessary adjustment. An interlock may be provided to prevent moving of the slide 137 prior to disengagement of the letterset relief plate on plate cylinder 130 from the blanket 125.

The top printing unit 10 has not been described in detail since such units are well known in the art; the bottom printing unit has been described only in so far as is necessary an understanding of the present invention which, in essence, utilizes as many standard and readily available parts and elements as possible. By modification of the impression cylinder, printing within the hollow of a concave structure, such as the inside of the lid of an egg carton is made possible.

Various changes and modifications may be made within the inventive concept, depending on size and shape of the structure to be printed on, that is the depth of the hollow, the angle of its confining walls or in the material on which the printing is to be effected, color and ink requirements and the like. While offset printing is both inexpensive and efficient, and effective on a wide variety of surfaces, the blanket cylinder 20, as well as the segmental cylindrical element may be replaced by a raised letter printing drum and a raised letter segmental cylindrical element, respectively, the letterset relief plates and cylinders then being replaced by ink transfer rolls. For printing on surfaces with a wide choice of design patterns, such as would occur in a printing operation printing names, trademarks and advertising for a large number of customers, the rotary offset system described in detail has been found to be preferred.

The apparatus of the present invention thus provides the capability of printing instructions, messages, advertising, dates, warning notices and the like on the inside of concave surfaces, such as the lids of boxes, or cartons and specifically egg cartons. The surface available to transmit information is effectively doubled without requiring additional information carriers, such as inserts, or paste-in sheets or the like. The information printed on the inside will be immediately visible upon opening of the carton and thus stand out. The present invention enables additional printing on the inside of a box already manufactured; and printing on the inside of lids of molded structures which never had a pair of flat printable surfaces.

I claim:

1. Apparatus to print on both sides of the lids of egg cartons comprising a table structure having a supply and a removal surface (62);

a first printing station comprising an offset printing cylinder (20) having a printing blanket (25), a plurality of assemblies of ink trains (40) and offset printing cylinders and plates (30), each adapted to print with a selected color, in ink transfer engagement with said printing blanket;

a second printing station, comprising a segmental cylindrical element (120) having a hub portion (124) and a pair of segmental cylindrical surface portions (121, 121') with leading (122) and trailing (123) faces joining said cylindrical and said hub portions and forming an angle in the order of 90 or less with the tangent of the segmental cylindrical surface at the junction of said surface to provide clearance and permit entry of said segmental cylindrical surface portions into the hollow of the lid of the egg carton, and printing blanket strips (125, 125') covering the cylindrical segmental surface portions (121, 121) of said element (120), and at least one assembly of an ink train (140) and an offset printin'g cylinder plate (130) located in ink transfer engagement with the printing blanket (125, 125') on the segmental cylindrical surface;

- said first and second printing stations being located with the axes of the printing cylinder and the segmental cylindrical element in alignment transverse to said table;

the offset assemblies of ink trains and offset printing cylinder plates being similar;

continuously movable conveyor means engaging open egg cartons with the lid convex surface (SX) facing a first direction and the concave surface (SV) facing the opposite direction lengthwise of said surfaces to feed said cartons to said printing stations and away from said printing stations;

and drive means in continuous, synchronous driving engagement with said carton conveyor means and said printing stations and driving the cylindrical printing surfaces of the printing stations at a slightly different surface speed from the continuous, linear transport speed of said carton conveyor means.

2. Apparatus according to claim 1 wherein said egg cartons are of expanded polystyrene.

3. Combination according to claim 2 wherein the surface clearance between the printing cylinder and the cylindrical elements is about 50 percent of the nominal thickness of the polystyrene egg carton material.

4. Apparatus according to claim 1 wherein said carton engaging conveyor means comprises continuously moving pusher elements (60, 61) engaging and delivering said cartons to said printing cylinder (20) and the segmental cylindrical element and removing said articles from said cylinder and segmental element after printing; said pusher elements being driven in synchronism with said drive means and at a linear speed slightly slower than the circumferential linear speed of said printing blanket (25) and said printing blanket strips (125, to prevent engagement of said cartons by said pusher elements during printing.

5. Apparatus according to claim 1 in which the egg cartons are of compressible material having thicknesses substantially varying from nominal value, and wherein the surface clearance between the printing cylinder and cylindrical elements is about 50 percent of the nominal thickness of the egg carton material. 

1. Apparatus to print on both sides of the lids of egg cartons comprising a table structure having a supply and a removal surface (62); a first printing station comprising an offset printing cylinder (20) having a printing blanket (25), a plurality of assemblies of ink trains (40) and offset printing cylinders and plates (30), each adapted to print with a selected color, in ink transfer engagement with said printing blanket; a second printing station, comprising a segmental cylindrical element (120) having a hub portion (124) and a pair of segmental cylindrical surface portions (121, 121'') with leading (122) and trailing (123) faces joining said cylindrical and said hub portions and forming an angle in the order of 90* or less with the tangent of the segmental cylindrical surface at the junction of said surface to provide clearance and permit entry of said segmental cylindrical surface portions into the hollow of the lid of the egg carton, and printing blanket strips (125, 125'') covering the cylindrical segmental surface portions (121, 121'') of said element (120), and at least one assembly of an ink train (140) and an offset printing cylinder plate (130) located in ink transfer engagement with the printing blanket (125, 125'') on the segmental cylindrical surface; said first and second printing stations being located with the axes of the printing cylinder and the segmental cylindrical element in alignment transverse to said table; the offset assemblies of ink trains and offset printing cylinder plates being similar; continuously movable conveyor means engaging open egg cartons with the lid convex surface (SX) facing a first direction and the concave surface (SV) facing the opposite direction lengthwise of said surfaces to feed said cartons to said printing stations and away from said printing stations; and drive means in continuous, synchronous driving engagement with said carton conveyor means and said printing stations and driving the cylindrical printing surfaces of the printing stations at a slightly different surface speed from the continuous, linear transport speed of said carton conveyor means.
 2. Apparatus according to claim 1 wherein said egg cartons are of expanded polystyrene.
 3. Combination according to claim 2 wherein the surface clearance between the printing cylinder and the cylindriCal elements is about 50% of the nominal thickness of the polystyrene egg carton material.
 4. Apparatus according to claim 1 wherein said carton engaging conveyor means comprises continuously moving pusher elements (60, 61) engaging and delivering said cartons to said printing cylinder (20) and the segmental cylindrical element (120), and removing said articles from said cylinder and segmental element after printing; said pusher elements being driven in synchronism with said drive means and at a linear speed slightly slower than the circumferential linear speed of said printing blanket (25) and said printing blanket strips (125, 125'') to prevent engagement of said cartons by said pusher elements during printing.
 5. Apparatus according to claim 1 in which the egg cartons are of compressible material having thicknesses substantially varying from nominal value, and wherein the surface clearance between the printing cylinder and cylindrical elements is about 50% of the nominal thickness of the egg carton material. 